MESSRS. HiVNCOCK AND EMBLETON ON THE ANATOMY OF DORIS. 
225 
all the genitalia except the ovary, and a network of its fine ramifications, when in- 
jected, can be seen spread over the surface of the mucus-gland. The aorta next 
passes forward and gains the median line beneath the buccal mass, and is resolved 
into two branches, a buccal and a pedial, the former going to the buccal mass and 
channel of the mouth ; the latter, dividing as it goes, runs backward on the floor of 
the visceral cavity, supplying the foot from end to end. 
In the viscera, except in the liver and in the skin, after repeated injections and 
examinations, we have failed to discover veins, and must therefore conclude that the 
blood, after having passed through the network of arterial ramifications, falls into 
spaces or sinuses, among the tissues, between the viscera and in the general peritoneal 
cavity. We are unable as yet to say whether the spaces into which the blood thus 
escapes are or are not provided with a delicate proper lining membrane, as has been 
advanced by M. leDr. Robin in his admirable ‘Rapport a la Societe de Biologie sur 
le Phlebenterisme, 1851.’ The general peritoneal cavity communicates freely by many 
apertures with a network of canals or sinuses in the skin, but we have as yet found 
no veins leading from the general cavity of the body directly to the respiratory organ. 
The spongy network of sinuses in the skin opens freely and widely into a great trunk 
sinus, running backward on each side of the body at the angle of union of the mantle 
with the foot. These trunks, opposite the posterior angles of the auricle, turn sud- 
denly inwards, perforate the inner surface of the skin, gaining the general cavity of 
the body ; they then, in the form of distinct systemic veins, penetrate the pericardium 
and empty themselves into the auricular cavity. Thus the blood current which we 
have traced from the heart along the arterial system through the sinuses of the 
visceral cavity and the skin, is brought by venous canals through the skin back at 
once to the heart without having previously passed through the branchise. 
How then, it will be asked, does the blood of Doris find its way to the branchise? 
It will be remembered we have accounted for the return to the heart of all the blood 
sent to the skin, and to the viscera, with the exception of the liver-mass ; now it is 
that portion of the blood which has circulated through the liver-mass, and that only, 
which is made to traverse the specialized respiratory apparatus before reaching the 
heart. We before mentioned that the arteries distributed to the liver-mass can be 
seen to form on its exterior a delicate and minute network ; we find by injection 
that the veins of this organ are similarly arranged, and that the principal branches 
of the arteries and veins run commonly side by side ; moreover, we have succeeded 
in filling numerous arteiial plexuses by injecting coloured fluid by the veins ; here 
these sinuses or lacunie must be reduced to their minimum, if indeed they exist at 
all. The principal venous branches of the liver converge and unite in a common 
hepatic trunk situated on the median line, at first concealed in the substance of the 
organ, and then in its backward course emerging at a groove at the posterior end of 
the liver. This trunk then turns upward and opens widely into the anterior limbus 
2 G 2 
